For modern optical high-performance facilities the requirements in relation to the imaging accuracy and resolution become higher and higher. This means on the one hand that larger and larger imaging respectively projection areas are attained; however on the other hand that the structures to be imaged have to be imaged more and more in smaller dimensions and in higher point and detail accuracy. Because of this reason it is necessary to expose with smaller and smaller wavelengths, i.e. with light having higher energy, which increases the energetic load of the optical elements. Moreover for a variety of technical applications, such as for example for micro lithography, for increasing the production rate shorter and shorter exposure times are demanded by which the radiant power respectively the radiation density which is directed through the optical facility, i.e. radiation exposure per time, has to rise involuntarily. Moreover for optical systems, in particular in communications engineering and telecommunications, a high luminous efficiency, i.e. a high transmission, is an important aim.
This means not only high requirements for the development of the respective optical facilities, but also for the material used for the optical facility which normally is a glass. Thus e.g. it is known that the use of high energy densities leads to a phenomenon which is called solarization by which the transmission, i.e. the radiolucency of an optical element, decreases drastically. However not only the total luminous efficiency of an optical element is reduced with that, but increasing amounts of energy are introduced into the matrix of the optical element by the radiation absorbed in this connection. Such a deposition of energy into the matrix additionally leads to compaction, i.e. a densification of the optical material. This densification causes shrinkage of the material matrix which also leads to a change of the optical properties, in particular the refraction power. But such changes of the refraction power result in a change of the radiation path which originally was calculated for the optical element by which the structure to be imaged will become blurred, i.e. the imaging accuracy will be lowered.
This effect is also enhanced, because such compactions are in a proportional ratio to the radiation and to the deposited energy, respectively, and each single component as well as also local areas inside these elements of an optical system are subjected to a different radiation exposure. Because of that in an optical system a geometrically irregular distortion takes place which adds in the total lenses. Thus during usage these effects lead to a strong decrease of the attainable point resolution as well as the image sharpness.
Since due to improved techniques such systems have a longer operating life today, also an increased radiation time of the optical elements occurs by which their energetic load increases and their time of application and hence their amortization and their viable use, respectively, will be limited which again leads to higher costs.